In factories and the like where industrial machinery is installed, in order to ensure the safety of an operator in cases such as where a fault occurs during operation of machinery, an emergency stop switch for emergency stop of the machinery is necessarily provided.
Heretofore, such an emergency stop switch incorporates; a first switch section provided with normally closed contact points which are normally on and which are switched off by push button operation at the time of an emergency, and a second switch section provided with normally open contact points which are normally off and which are switched on by operation of the push button at the time of an emergency, and the first and second switch sections are operated linked together. At normal times, the normally closed contact points of the first switch section are switched on by spring force, and the normally open contact points of the second switch section are switched off by spring force. The construction is such that when at the time of an emergency the push button is operated, the normally closed contact points of the first switch section go off, and the normally open contact points of the second switch section come on.
Here, the normally closed contact points output from the first switch section is generally used as a reset input to a self hold circuit provided in the operating control circuit for the machinery. That is to say, if the normally closed contact points are once switched off, the self hold circuit is reset, so that after this, provided that a trigger input signal is not input to the self hold circuit by some other separate means, then, even if the normally closed contact points of the first switch section are again switched on by spring force, an output from the self hold circuit is not produced. Recently, there is also the case where this is managed by simply inputting to a monitor.
This type of emergency stop switch is installed at each work site in a factory, and has heretofore been wired as shown in FIG. 1.
That is to say, respective first switch portions 2.sub.1.about.2n of a plurality of emergency stop switches 1.sub.1.about.1.sub.n are connected in series to a machinery operation control circuit 6 via a relay terminal assembly 4. Furthermore, respective second switch sections 3.sub.1.about.3.sub.n are separately connected to a monitor 5 via the relay terminal assembly 4. These emergency stop switches 1.sub.1.about..sub.n are installed at each respective work site in a factory.
Consequently, in the case where none of the emergency stop switches 1.sub.1.about.1.sub.n are operated, the operation control circuit 6 generates an operation output for the machinery as normal. However if any one of the emergency stop switches 1.sub.1.about.1.sub.n is operated, then the relevant first switch section switches off so that the operation output from the operation control circuit 6 stops. At the same time, the second switch section of the operated emergency stop switch switches on so that the work site where the emergency stop switch is operated is shown on the monitor 5, enabling the work site where the emergency situation occurred to be made known.
However, with the conventional emergency stop switch, due to the construction using electric contact points, there is the possibility of a contact point fusion fault occurring. Since the emergency stop switch is only used in the case where an emergency situation arises, and is thus not frequently operated, monitoring to determine if it will operate normally is difficult. Moreover, even if inspected individually, since there is a large number disposed within a factory, then the time taken is considerable. Therefore, there is the danger that contact point fusion faults can be overlooked, and if the normally closed contact points of the first switch section have a fusion fault, then even if the push button is operated, the operation output for the machinery cannot be stopped, thus posing a problem from the point of ensuring operator safety.
Moreover, the work site where the emergency stop switch circuit as shown in FIG. 1 with emergency stop switches severally connected is installed, and the machinery operation control side where the operation control circuit 6, the relay terminal assembly 4 and the monitor 5 and so on are installed, are detached from each other. Hence in the case of a switch circuit which utilizes emergency stop switches using conventional electrical contact points, then as shown in FIG. 1, it is necessary for the respective emergency stop switches 1.sub.1.about.1.sub.n installed at the respective work sites to be connected in series via the relay terminal assembly 4, and also the location of all of the emergency stop switches 1.sub.1 .about.1.sub.n must be notified individually to the monitor 5 via the relay terminal assembly 4. Therefore, there is the problem that the number of wires for connecting between the emergency stop switches 1.sub.1.about.1.sub.n and the relay terminal assembly 4 is considerable.
The present invention takes into consideration the above situation, with the object of providing an emergency stop switch having no contact points so that there is no possibility of contact point fusion faults. Moreover, it is an object to provide an emergency stop switch circuit which does not incur an increase in wiring even in the case where a switch circuit connected to a plurality of emergency stop switches is installed. Furthermore, it is an object to provide an emergency stop switch circuit wherein monitoring for normalcy of the respective emergency stop switches is facilitated.